Abstract
Constitutional conventions are properties of constitutional systems that regulate often important areas of activity. Constitutional conventions typically lack legal force, but they are rarely openly abrogated in established democracies, especially Westminster systems. Yet while constitutional actors are generally loath to reject long-held convention rules entirely, they are inclined to resist them. This chapter examines how actors justify resisting and even departing from a convention rule and how this affects the consequent development of that convention. It does so through an analysis of claims presented by opposition peers challenging the UK's Salisbury-Addison convention in the period between 1945 and 2021. We find that actors rarely challenge the legitimacy of the convention but might make claims to an exemption that enables them to resist some aspect of the convention. Exemption claims are, however, generally consistent with the convention's value parameters and make possible the gradual evolution of the convention without threatening its legitimacy.